This invention relates to sealing devices disposed relative to two generally stationary structures of approximately cylindrical shape as well as to other objects such as two relatively rotating members requiring a fluid seal therebetween. The present invention may provide for air sealing of ceramic combustor liners that typically have large temperature excursions as well as excessive surface temperature that may exceed the temperature capability of metallic sealing devices and that may experience deflection relative to the adjacent structure. The device also may be used to provide fluid sealing between a rotating shaft and a housing circumscribing the rotating shaft.
The present art uses a series of interlocking ceramic segments disposed around a combustor liner for sealing. The ceramic segments may be biased against the combustor by metallic springs or fingers. This seal structure provides air-to-air sealing between the two elements while allowing axial and radial relative motions between the bodies. Seals that use a spring loading feature in other sealing applications may be as disclosed in U.S. Pat. No. 4,415,317; however, they are expensive to manufacture, subject to premature failure of individual spring elements and are complex to install in the application.
Use of ceramic materials for seals has been hypothesized for brush type seals in U.S. Pat. No. 4,600,202. This patent discloses a brush type seal between machine components in relative motion, of which at least one member rotates, in which strands or bristles consist of composite fibers designed for good thermal conductivity in at least portions of their surface and at least a portion has flexible, elastic properties. The disclosure indicates the bristles can be made from various types of glass, glass-metals, glass-ceramics, or a combination thereof. However, this proposed type of bristle seal with ceramic content flexible enough to perform as a seal and not fracture in use has been found to be difficult to manufacture and to have low reliability in application.
Laminated finger seals are known in the art as exemplified by U.S. Pat. No. 5,108,116. These seals are designed for fluid sealing between relatively rotating elements as for example a shaft and a housing. As a result of this application, the fingers, which may have a foot element, are designed to slide on the shaft element when rotating. The finger portion provides pressure through the foot portion to maintain contact with the rotating shaft. A balance must be maintained to avoid excessive wear of the foot portion and the rotating shaft. There exist various improvements in designs for the foot portion, as for example to give it aerodynamic properties to glide over the surface of the shaft. In such an application a considerable amount of pressure can be exerted by the finger elements to maintain a tight seal interface and aerodynamic or sliding motion at low friction levels is not required. However, the use of a ceramic composition as in the instant invention includes a ceramic finger seal that can withstand the excessive heat generation caused by the friction between the seal and the rotating shaft.
For the combustion liner type interface sealing application, the combustor liner in operation may be at an elevated temperature relative to the surrounding structure. A finger seal inserted therebetween may have the finger elements extended radial outward for engagement with the combustor liner. The inner circumference of the seal may then be attached to the housing. Use of ceramic composition finger seals allows application of such combustion liner seals to be used in very high temperature environment. For combustion liner applications the ceramic composition finger seals may be fabricated with the finger elements oriented radial inward for sealing the outer most portion of the combustor.
As can be seen, there is a need for a generally circular sealing device for air and fluid sealing between two bodies experiencing relative radial or axial motion and elevated temperatures.
In one aspect of the present invention, a set of laminated ceramic finger seal may be inserted between two generally stationary structures to inhibit airflow therebetween. The seal may have multiple diaphragm segments and diaphragm members laminated together and fixed in a holding device. The diaphragm members may be circumferential bands having a generally continuous inside diameter portion and a segmented outside diameter portion or a reverse orientation thereof and may be designated as inside diameter and outside diameter seals.
The segmented portion defines a circumferentially uniform array of finger elements spaced apart to define a plurality of uniform gaps. When the seal is clamped in the holding device attached to the housing and assembled into the combustor the finger elements are deflected toward the inner circumference of the ceramic finger seal thereby applying pressure against the combustor liner wall to affect the sealing between the structures. For use in sealing the outermost portion of the combustor the finger elements are deflected toward the outer circumference of the ceramic finger seal.
With relative rotating elements the circumferential bands may have a general continuous outside diameter portion and a segmented inside diameter portion. The finger elements with a foot portion contact the rotatable shaft to apply pressure to effect the sealing between the structures.
In another aspect of the present invention, the uniform gaps of the diaphragm members may have a stress reducing keyhole formed at the terminal end thereof. The diaphragm members may be laminated together with a high temperature joining compound and disposed between a pair of spacers with the combination clamped between a pair of endplates.
In a further aspect of the present invention, the finger elements have a foot portion at an outermost end for sealing engagement with a combustor liner or a rotating shaft.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.